Radio link control reset using radio resource control signaling

ABSTRACT

A method and apparatus are described for implementing a reset procedure for radio link control (RLC) using radio resource control (RRC) signaling. A wireless transmit/receive unit (WTRU) receives a request for RLC reset. A processor at the WTRU comprises a RRC entity and a RLC entity. The RRC entity receives the request for a RLC reset in a radio resource control message. The RLC entity reassembles RLC service data units (SDUs) from any protocol data units (PDUs) that are received out of sequence at a receiving side of the RLC entity. The reassembled SDUs are delivered in sequence to a packet data convergence protocol entity (PDCP). At the receiving side of the RLC entity, any remaining PDUs that are not able to be reassembled are discarded. At a transmitting side of the RLC entity, all SDUs and PDUs stored in transmit buffers are discarded.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. non-provisional applicationSer. No. 12/346,443 filed on Dec. 30, 2008, which claims the benefit ofU.S. Provisional Application No. 61/019,049 filed on Jan. 4, 2008, whichis incorporated by reference as if fully set forth herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

Current efforts for the 3^(rd) Generation Partnership Project (3GPP)Long Term Evolution (LTE) and LTE-Advanced wireless communicationprograms are to bring new technology, new architecture and new methodsin the new LTE settings and configurations in order to provide improvedspectral efficiency and reduced latency. As a result, the radioresources would be better utilized to bring faster user experiences andricher applications and services with less cost.

As part of this effort, 3GPP is defining new procedures for the RadioResource Control (RRC) and Radio Link Control (RLC) layers to help meetthese goals. In the prior art (e.g., Universal Mobile TelecommunicationSystem (UMTS) specifications), an RLC entity of a transmitter did notrequest a reset after reaching a maximum allowed number of RLCretransmissions. Instead, the RLC entity would attempt to keep the callalive and initiate its own reset without the RRC being aware. To do so,the RLC entity would continue retransmissions and then continue with thereset procedure until the RLC was able to recover or until the maximumnumber of retransmission for RLC reset was reached. When the RLC failed,the RRC would initiate a radio link failure (RLF) recovery procedure,but would put the transmitter into IDLE mode rather than attempting aRRC connection re-establishment.

Current LTE proposals allow a RLC entity to reset using RLC controlprotocol data units (PDUs). However, this procedure can be complex.Accordingly, there exists a need for an improved method and apparatusfor resetting the RLC entity.

SUMMARY

A method and apparatus are described wherein a reset procedure for aradio link control (RLC) is implemented by radio resource control (RRC)signaling. Triggers for the initiation and execution of the resetprocedure are also described.

A wireless transmit/receive unit (WTRU) may be configured to reset abase station radio link control (RLC) entity. An RLC entity in the WTRUmay be configured to detect that a number of retransmissions has reacheda maximum number of allowed retransmissions, and trigger a radio linkfailure. A radio resource control (RRC) entity in the WTRU may beconfigured to send an RRC message indicating an RLC reset to a basestation in response to the radio link failure indication. The RRCmessage may include an information element identifying a radio linkentity requesting the RLC reset, a radio link entity to be reset, areset sequence number, a cause for the RLC reset, or configurationparameters for the RLC reset.

Alternatively, a wireless transmit/receive unit (WTRU) receives arequest for radio link control reset. A processor at the WTRU comprisesa radio resource control (RRC) entity and a radio link control (RLC)entity. The RRC entity receives the request for a radio link controlreset in a radio resource control message. The RLC entity reassemblesradio link control service data units (SDUs) from any protocol dataunits (PDUs) that are received out of sequence at a receiving side ofthe RLC entity. The reassembled SDUs are delivered in sequence to apacket data convergence protocol entity. At the receiving side of theRLC entity, any remaining PDUs that are not able to be reassembled arediscarded. At a transmitting side of the RLC entity, all SDUs and PDUsstored in transmit buffers are discarded.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example and to be understood in conjunction with theaccompanying drawings wherein:

FIG. 1 is a functional block diagram of a transmitter and receiverconfigured to perform a RLC reset;

FIG. 2 is a functional block diagram of a transmitter processor and areceiver processor configured to perform a RLC reset; and

FIG. 3 is signal diagram for a Protocol Reset signal.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, an evolved Node-B, a site controller, an accesspoint (AP), or any other type of interfacing device capable of operatingin a wireless environment.

It should be noted that the disclosed RLC ‘Reset’ procedure may bereferred to by other names such as RLC ‘Re-establishment’ or RLC‘Re-configuration’. As such, the disclosed method and apparatus applieseven when the procedures proposed herein are described using other namesor terms in the 3GPP standards specifications.

FIG. 1 is a functional block diagram of a transmitter and receiver 110,120 configured to perform the disclosed method. In addition tocomponents included in a typical transmitter/receiver (i.e., a WTRU orbase station), the transmitter 110 and the receiver 120 includes:processors 115, 125 configured to perform a reset of an RLC entity usingRRC signaling; receivers 116, 126 in communication with processors 115,125; transmitters 117, 127 in communication with processors 115, 125;and antennas 118, 128 in communication with receivers 116, 126 andtransmitters 117, 127 to facilitate the transmission and reception ofwireless data. Additionally, the receiver 116, the transmitter 117 andthe antenna 118 may be a single receiver, transmitter and antenna, ormay include a plurality of individual receivers, transmitters andantennas, respectively. The transmitter 110 may be a WTRU transmittingto a base station receiver 120. Alternatively, the transmitter 110 maybe a base station transmitting to a WTRU receiver 120.

FIG. 2 shows a signaling diagram for the transmitter 110 and thereceiver 120, in which the processor 115 comprises a radio link controllayer (RLC) entity 221, a radio resource control layer (RRC) entity 222,a packet data convergence protocol layer (PDCP) entity 223, and theprocessor 125 comprises an RLC entity 231, a RRC entity 232, and a PDCPentity 233. While a single RLC entity 221 is shown for the processor115, and a single RLC entity 231 is shown for the processor 125, theremay be multiple RLC entities, including a transmitting UnacknowledgedMode (UM) RLC entity, a receiving UM RLC entity, a transmittingTransparent Mode (TM) RLC entity, a receiving TM RLC entity, and anAcknowledged Mode (AM) RLC entity. A single RLC entity 221, 231 is shownfor purpose of simplifying the description herein and is not meant torepresent a limitation to the disclosed method and apparatus. It shouldbe noted that the inter-layer entity activity disclosed below for theRadio Resource Control (RRC) and RLC may be accomplished by defining newprimitives or information elements between the layers.

Upon detecting an RLC Reset trigger as an indication of RLC failure, theRLC entity 221 included in transmitter processor 115 sends a RLC resetrequest indication 201 to the RRC entity 222 indicating that a RLC Resetis desired (i.e., that both the peer RLC entity 231 and the RLC entity221 itself should be reset). An example of an RLC Reset trigger may be,for an AM RLC entity 221, that the maximum number of retransmissionsallowed has been reached. Other examples of triggers include a ServiceData Unit (SDU) discard not being configured for an event, RLC StatusPDUs indicating erroneous sequence numbers; unrecoverable errors; andany other event or trigger that requires the RLC to be reset.

The RLC Reset request indication 201 that is forwarded to the RRC entity222 may include one or more of the following types of requestinformation in the form of an information element (IE) or a single ormultiple bit value. A cause value may be included to indicate the reasonfor the RLC Reset request indication 201. For example, if the trigger isthe maximum number of retransmissions being reached, the RLC resetrequest indication 201 includes an indication of this to the RRC entity222. Status information may also be included in the RLC Reset requestindication 201 indicating the last sequence number (SN) correctlyreceived for the RLC entity 221 requesting the RLC Reset. The RLC Resetrequest indication 201 may also include an identification of the RLCentity 221 to be reset (e.g., the RLC entity identification may beaccording to the logical channel instance associated with the RLC entityor the radio bearer associated with the RLC entity), or alternatively, anew RLC entity ID may be defined and indicated for explicitlyidentifying the RLC entity.

After forwarding the RLC request indication 201 to the RRC entity 222,the RLC entity 221 may perform one or more of the following:

-   -   1. Start a timer T101 that may be specific to each RLC entity        221 or common to each RLC entity 221.    -   2. Suspend transmission of any protocol data units (PDUs) on the        RLC entity 221 being reset.    -   3. Flush the buffer of any SDUs sent before the RLC reset.    -   4. Suspend reception of any PDUs on the RLC entity 221, which        may occur via discarding any received PDUs for such entity.    -   5. Increment/Decrement a counter C101 that keeps a count of the        number of reset requests. This counter may be specific to each        RLC entity.    -   6. Reset the RLC entity 221 to initially configured parameters        (e.g., the sequence number (SN) may be reset back to zero).        Alternatively, the RLC entity 221 may take this reset action on        the expiration of the timer T101.    -   7. Wait for an indication 202 from the RRC entity 222 before        starting any of the above procedures. The indication 202 from        the RRC entity 222 may take the form of an acknowledgment of the        reset request indication 201 and/or confirmation of the reset        procedures being initiated by the RRC entity 222.

The RRC entity 222, upon receiving an RLC reset indication 201 that anRLC reset is required, may send an RRC message 203 to the peer RRCentity 232 indicating a reset of RLC is required. The parameters for theRLC reset may be included in any RRC message 203 (e.g., a RRC CONNECTIONRE-ESTABLISHMENT message or a RRC CONNECTION RECONFIGURATION message) orin a new RRC message dedicated for reset procedures, such as a PROTOCOLRESET message as will be described further below. In order to transmitthe RLC Reset request information, a new IE, such as an RLC Reset IE ora Protocol Reset Indicator Information Element (IE), may be used forindicating the reset request of the RLC entity 221. This IE may becarried in any RRC message 203 or in a specific message dedicated forreset procedures. An example of the RLC Reset IE parameters is presentedin Table 1 below.

TABLE 1 Type and Information Multi Reference Semantics Information for<1 to protocol entity Number of for reset entities requestingReset> >Protocol Boolean Identifies whether the entity entity beingreset is a PDCP entity or requesting an RLC entity. This may not bereset necessary if the reset indicator IE is defined specifically forRLC or PDCP. >>Identity Integer Identification of the RLC entity beingreset. This may be either the logical channel instance mapped to the RLCentity, or the RB ID mapped to the entity or some other ID. Thisinformation may be implied by the presence of some other information ina parent field in the information tree. >>>RSN Integer The Resetsequence number (RSN) identifies if this is the first reset request forthis entity or a retransmission. Alternatively, the RSN may be definedfor the entire RRC message instead of on a per- entity basis >>>CauseInteger Indicates the reason for reset request >>>Reset BooleanIdentifies if the RLC entity is to configuration be reset todefault/initial configurations or some different configuration If RLCentity is to be reset to a >>>>Param- configuration different from etersfor initial/default. reset

The individual IEs described in TABLE 1 are optional and the informationcontained in them may be passed in a different manner. The RRC message203 indicating the reset may be any indication of a reset. For example,the RRC message 203 may include, but is not limited to, a bit, or a fewbits, that may be passed in any RRC message to more detailed IEs (e.g.,see Protocol Reset Indicator IE) to dedicated messages. The indicationsin the RRC message 203 may be explicit or implicit and may also includeRLC and/or PDCP status. For an implicit indication, a separately sentRRC message that does not contain the reset IEs may indicate that areset is required merely by the RRC message name according to aprearranged definition.

The RRC message 203 indicating the RLC reset request to the peer RRCentity 232 may include an explicit or implicit indication of the time ofthe reset/activation of reset. Alternatively this may be accomplished ona Transmission Time Interval (TTI) or a System Frame Number (SFN) basis.As an example, a synchronization may be achieved by alignment of the RLCreset with the SFN or a number of TTIs relative to the last TTI in whichthe RRC message 203 was transmitted/received.

In the event that the RLC entity 221 to be reset is the same RLC entitythat would initiate an RRC message 203 indicating the reset, the RRCentity 222 may transmit the message indicating the reset over a radiobearer (RB), which is mapped to a different RLC entity of transmitter110. Alternatively, a new RB and associated RLC entity may beconfigured. Alternatively, the RRC message 203 containing the RLC resetIE can be transmitted on a Signaling RB (SRB). This SRB may be dedicatedto the reset of RLC and some other purposes (e.g., a reset of PDCP). Itis preferable that the SRB be mapped to a RLC UM entity to avoid thepossibility of this SRB being reset.

The RRC entity 222 may ensure that the RRC message 203 for RLC Resetwill fit inside a single RLC PDU. The RRC entity 222 may aggregatemultiple reset requests from different RLC entities 221 into a singlemessage 203. If the transmitting RRC entity 222 receives a reset requestfor a transmitting RLC entity 221 for which a reset procedure is ongoingit may ignore the request. The transmitting RRC entity 222 mayacknowledge a reset request from the transmitting RLC layer/entity in anacknowledgment signal 202.

The transmitting RRC entity 222 may send a pending RLC Reset indication204 to the PDCP entity 223. This may trigger the generation of a PDCPstatus PDU at the transmitter 110.

After transmission of the RRC message 203 indicating the RLC Resetrequest, the RRC entity 222 may perform one or more of the following:

-   -   1. Start a timer T102 timer that may determine the time the        transmitting RRC entity 222 may wait for an RLC Reset        acknowledgment 213 before initiating further action;    -   2. Increment/Decrement a counter C102 that keeps a count of the        number of RLC reset requests via the RRC messages 203. This        counter may be specific to each RLC entity 221 and may be used        to indicate the RSN for the RLC Reset request. The RRC entity        222 may use a RRC Transaction Identifier to distinguish        re-transmissions of the same reset request; and    -   3. Provide an indication 205 to the RLC entity 221 that the RLC        Reset procedure has been initiated.

If the timer T102 described above expires, the RRC entity 222 mayimplement one of the following:

-   -   1. Retransmit the RLC Reset request in another RRC message 203;    -   2. Send a new RLC Reset request, with possibly a reference to a        different RLC entity to be reset;    -   3. Increment/Decrement the counter C102 and restart the timer        T102; and    -   4. Provide an indication of timer T102 expiration to the RLC        entity 221.

If the counter C102 reaches a pre-determined value (e.g. aconfigured/pre-determined value for the maximum number of resetrequests) the RRC entity 221 may initiate a different set of procedures.For example, the RRC entity 222 may initiate RRC RECONFIGURATIONprocedures or Radio Link Failure procedures or Physical ChannelReconfiguration procedures or some other recovery procedure.

The RRC entity 222 may use Hybrid Automatic Repeat Request (HARQ)assistance to retransmit the RRC message 203 that contains the resetindicator. For example, a HARQ entity 224 may indicate to the RRC entity222 that delivery of the RRC PDU that contains the RLC reset has failed,and subsequently the RRC 222 retransmits the PDU.

At the receiver 115, upon receipt of the RRC message 203 with the RLCReset request, the RRC entity 232 implements one or more of thefollowing actions:

-   -   1. Send an RRC message acknowledgment 213 to acknowledge receipt        of the reset request back to the transmitter RRC entity 222. The        receiver RRC entity 232 may pass the RLC Reset request to the        receiver RLC entity 231; alternatively, the acknowledgment 213        may be sent after waiting for a reset confirmation from the RLC        entity 231;    -   2. Stop the transmission/reception of any PDUs on the RBs        configured for the RLC entity 231;    -   3. Instruct the RLC entity 231 to flush the RLC data buffer; and    -   4. Pass the RLC Reset request to the RLC entity 231 as        indication 211 and to the PDCP entity 233 as indication 214,        along with any associated reset parameters.

In the event that the RLC entity 231 that is to be reset is the same RLCentity that is to initiate the RRC message 213 indicating the RLC Resetacknowledgment, the receiver RRC entity 222 may transmit the messageindicating the reset acknowledgment over a RB which is mapped to adifferent RLC entity. Alternatively, a new RB and associated RLC entitymay be configured.

In another alternative, the RRC message 213 comprising the RLC Resetacknowledgment IE can be transmitted on a Signaling RB (SRB). This SRBmay be dedicated to the reset acknowledgment of RLC and some otherpurposes (e.g., reset acknowledgment of PDCP). This SRB may be mapped toa UM RLC entity to avoid the possibility of this SRB being reset.

The RRC entity 232 may ensure that the RRC message 213 for resetacknowledgment will fit inside a single RLC PDU. The RRC entity 232 mayaggregate multiple reset acknowledgments for different RLC entities 231into a single message.

The RRC procedure may use HARQ assistance to retransmit the RRC messagethat contains the reset acknowledgment indicator. For example, a HARQentity 234 may indicate to the RRC 232 that delivery of the RRC PDU thatcontains the RLC reset acknowledgment has failed, and subsequently theRRC entity 232 retransmits the PDU.

The RRC entity 232, upon receiving an RLC reset indication 212 that anRLC reset has occurred, may send an RRC message 213 to the peer RRCentity 222 indicating acknowledgment of the RLC reset. The parametersfor the RLC reset acknowledgment may be included in any RRC message 213(e.g., a RRC CONNECTION REESTABLISHMENT COMPLETE message or a RRCCONNECTION RECONFIGURATION COMPLETE message) or in a new RRC messagededicated for reset procedures, such as a PROTOCOL RESET ACKNOWLEDGEmessage as will be described further below. In order to transmit the RLCReset acknowledgment information, a new IE, such as an RLC ResetAcknowledgment IE or a Protocol Reset ACK IE, may be used for indicatingthe reset of the RLC entity 231. This IE may be carried in any RRCmessage 213 or in a specific message dedicated for RLC reset procedures.An example of the RLC Reset Acknowledgment IE parameters is presented inTABLE 2 below.

TABLE 2 Type and Information Multi Reference Semantics Information for<1 to Number of protocol entity entities for Reset reset being beingacked> acknowledged >Protocol entity Boolean Identifies whether theentity for reset being being reset acknowledged is a acknowledged PDCPentity or an RLC entity. This may not be necessary if the resetacknowledge indicator IE is defined specifically for RLC orPDCP. >>Identity Integer Identification of the RLC entity being resetacknowledged. This may be either the logical channel instance mapped tothe RLC entity, or the RB ID mapped to the entity or some other ID. Thisinformation may be implied by the presence of some other information ina parent field in the information tree. >>>RSN Integer The Reset SNidentifies the corresponding reset request that is being acked. Thisshall be the same as the RSN in the corresponding reset request.

It should be understood that the individual RLC Reset Acknowledge IEparameters described above are optional and the information contained inthe IE may be passed in a different manner.

When the RLC entity 231 at the receiver receives a command from the RRCentity 232 to reset, the RLC entity 231 may implement one or more of thefollowing:

-   -   1. Reset some or all the RLC state variables for that entity to        their initial/default values or to the value (if any) configured        in the reset request;    -   2. Reset configurable parameters to their configured values or        to a new value (if any) received in the reset request;    -   3. Stop and/or restart any or all timers associated with that        RLC entity 231;    -   4. In the receiving side of the RLC entity 231, if possible,        reassemble RLC SDUs from the PDUs that are received out of        sequence and deliver them to the upper layer entities (e.g.,        PDCP entity 233); discard any remaining PDUs that could not be        reassembled into RLC SDUs;    -   5. In the transmitting side of the RLC entity 231, discard all        RLC PDUs from the PDU (re)transmit buffer of the RLC entity 231;    -   6. In the transmitting side of the RLC entity 231, discard all        RLC SDUs from the SDU transmit buffer of the RLC entity 231, and        notify the upper layer entities (e.g., PDCP entity 233) of the        discarded SDU(s). After receiving such notification, the upper        layer (e.g., PDCP entity 233) may re-submit (i.e., effectively        retransmit) those SDUs for transmission to the RLC entity 231        below it, following the completion of the RLC reset. In another        alternative, in the transmitting side of the RLC entity 231, the        RLC SDUs are not discarded from the SDU transmit buffer of the        RLC entity 231 when reset occurs;    -   7. In the transmitting side of the RLC entity 231, notify the        upper layers (e.g., PDCP entity 233) of all SDUs whose reception        have not been acknowledged (confirmed) by the peer RLC entity        221 (via RLC STATUS PDUs). After receiving such notification,        the upper layer entity (e.g., PDCP entity 233) may re-submit        (i.e., effectively retransmit) those SDUs for transmission to        the RLC entity 231 below it, following the completion of the RLC        reset;    -   8. Confirm completion of the reset procedures to the RRC with        indication 212; and    -   9. Indicate the completion of reset to upper layer entities        (e.g., PDCP entity 233 with indication 215).

The PDCP entity 233 may use an indication of the RLC reset (received viaRRC indication 214 or RLC indication 215) to generate a PDCP Status PDU.

The RLC entity 231 reset may be synchronized with the RRC procedure(i.e., the RRC message 203 and/or message 213). The RRC procedure mayinclude an explicit or implicit indication of the time of thereset/activation of reset. Alternatively this may be accomplished on aTTI or SFN basis. As an example, the synchronization between the RRCprocedure and the RLC reset could also be aligned with the SFN or anumber of TTI's relative to the last TTI in which the RRC message 203and/or RRC message 213 was received.

Upon reception of the acknowledgment of the RLC reset via RRC message213 from the receiver RRC entity 232, the transmitter RRC entity 222implements one or more of the following:

-   -   1. Stop timer T102;    -   2. Reset the counter C102 to its initial value or zero; and    -   3. Confirm the acknowledgment RRC message 213 to the RLC entity        221 with indication 205 and to the PDCP entity 223 with        indication 206.

The RLC entity 221, upon receiving acknowledgment of the reset requestvia the RRC indication 205, implements one or more of the following:

-   -   1. Stop timer T101;    -   2. Reset counter C101 to zero;    -   3. Reset some or all the RLC state variables for that entity to        their initial/default values or to the value (if any) configured        in the reset request;    -   4. Reset configurable parameters to their configured values or        to a new value (if any) received in the reset request;    -   5. Stop and/or restart any or all timers associated with that        RLC entity 221;    -   6. In the receiving side of the RLC entity 221, if possible        reassemble RLC SDUs from the PDUs that are received out of        sequence and deliver them in sequence to the PDCP entity 223;        discard any remaining PDUs that could not be reassembled into        RLC SDUs;    -   7. In the transmitting side of the RLC entity 221, discard all        RLC PDUs from the PDU (re)transmit buffer of the RLC entity 221;    -   8. In the transmitting side of the RLC entity 221, discard all        RLC SDUs from the SDU transmit buffer of the RLC entity 221, and        notify the upper layers (e.g., PDCP 223) of the discarded        SDU(s). After receiving such notification, the upper layer        (e.g., PDCP 223) may re-submit (i.e. effectively retransmit)        those SDUs for transmission to the RLC entity 221 below it,        following the completion of the RLC reset. In another less        preferred alternative: In the transmitting side of the RLC        entity, do not discard RLC SDUs from the SDU transmit buffer of        the RLC entity 221 (when reset occurs);    -   9. In the transmitting side of the RLC entity 221, notify the        upper layers (e.g., PDCP 223) of all SDUs whose reception have        not been acknowledged (confirmed) by the peer RLC entity (via        RLC STATUS PDUs). After receiving such notification, the upper        layer (e.g., PDCP 223) may re-submit (i.e. effectively        retransmit) those SDUs for transmission to the RLC entity 221        below it, following the completion of the RLC reset;    -   10. Confirm completion of the reset procedures to the RRC entity        222; and    -   11. Indicate the completion of reset to upper layers (e.g. PDCP        223).

The PDCP entity 223 may use the acknowledgment of the RLC reset(received via RRC indication 206 or RLC indication 208) to generate aPDCP Status PDU.

The RLC 221 reset may be synchronized with the RRC procedure (i.e., theRRC message 203 and/or message 213). The RRC procedure may include anexplicit or implicit indication of the time of the reset/activation ofreset. Alternatively this may be accomplished on a TTI or SFN basis. Asan example the synchronization between the RRC procedure and the RLC 221reset could also be aligned with the SFN or a number of TTI's relativeto the last TTI in which the RRC message 203, and/or RRC message 213 wasreceived.

In accordance with the method disclosed above for RLC reset accomplishedvia RRC, the following is a summary of the RRC signaling for the RRCmessages 203 and 213 in terms of a Protocol Reset procedure, shown inFIG. 3.

The transmitting RRC entity 222 may initiate this Protocol Resetprocedure whenever the RLC entity 221 in the transmitter 110 indicatesthe need for resetting a RLC entity.

Upon initiation of the procedure the transmitting RRC entity 222:

-   -   1> Initiates transmission of a PROTOCOL RESET REQUEST message        301    -   1> Indicates initiation of the procedure to the RLC (optional)    -   1> Start Timer T102 when lower layers indicate successful        transmission of the message

Upon expiration of the timer T102 the transmitting RRC entity 222:

-   -   1> Re-Initiates transmission of the PROTOCOL RESET REQUEST        message 301

-   1> Re-Starts Timer T102 when lower layers indicate successful    transmission of the message

The transmitting RRC entity 222 takes the following actions when itinitiates the transmission of a PROTOCOL RESET REQUEST message 301:

-   -   1> if this is a new reset request        -   2> Initialize a new instance of the counter C102 and            increment it by one    -   1> If this is a reset request that is being re-transmitted        -   2> increment the counter C102 by one

The transmitting RRC entity 222 sets the contents of the PROTOCOL RESETmessage 301 as follows:

-   0> If C102 counter is <=MaxNumberofResetReTransmissions+1    -   1> Identify the RLC entities to be reset in the PROTOCOL RESET        REQUEST message 301 and set the Transaction Identifier in the        message to be equal to the value of the C102 counter-   0> else    -   1> Declare RL failure and start the RL failure handling        procedure.    -   2> Try to re-establish the connection by sending the RRC        re-establishment request

Upon receiving a PROTOCOL RESET REQUEST message 301 the RRC entity 232:

-   -   1> Initiates transmission of the PROTOCOL RESET ACKNOWLEDGE        message 302    -   1> Passes the reset request to the RLC entity 231    -   1> Starts timer T103 when lower layers indicate successful        transmission of the message (optional)        The RRC entity 232 sets the contents of the PROTOCOL RESET        ACKNOWLEDGE message 302 as follows:    -   1> Set the Transaction Identifier value of the message to the        corresponding Transaction Identifier in the PROTOCOL RESET        REQUEST message 301 being acknowledged

Upon receiving a PROTOCOL RESET ACKNOWLEDGE 302, the RRC entity 222:

-   -   1> Stops timer T102    -   1> Resets counter C102 to zero    -   1> Initiates transmission of the PROTOCOL RESET COMPLETE message        303 (optional)    -   1> Indicate receipt of the acknowledgment to the lower layers        (e.g. RLC)

The following is a summary of the messages depicted in FIG. 3.

The PROTOCOL RESET REQUEST message 301 is used for requesting a reset ofa lower-layer protocol entity:

Signaling radio bearer: SRB 1 or SRB 2

RLC-SAP: AM or UM

Logical channel: DCCH

Direction: UE->E-UTRAN, EUTRAN->UE

Name Need Type/reference Message Type MP <ref> Transaction identifier MPInteger [0 . . . 3] Protocol Reset Indicator IE MP

The PROTOCOL RESET ACKNOWLEDGMENT message 302 is used for acknowledginga reset of a lower-layer protocol entity:

Signaling radio bearer: SRB 1 or SRB 2

RLC-SAP: AM or UM

Logical channel: DCCH

Direction: UE->E-UTRAN, EUTRAN->UE

Name Need Type/reference Message Type MP <ref> Transaction identifier MPInteger [0 . . . 3] Protocol Reset Ack IE MP

The PROTOCOL RESET COMPLETE message 303 is used for completing a resetof a lower-layer protocol entity (optional):

Signaling radio bearer: SRB 1 or SRB 2

RLC-SAP: AM or UM

Logical channel: DCCH

Direction: UE->E-UTRAN, EUTRAN->UE

Name Need Type/reference Message Type MP <ref> Transaction identifier MPInteger [0 . . . 3]

The disclosed methods and apparatuses are applicable to any wirelesscommunication devices and systems, including those related to 3GPP LTEand/or HSPA enhancements (e.g. WCDMA evolution Rel-7, Rel-8, etc).

Although the features and elements are described in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided may beimplemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A method implemented by a wireless transmit/receive unit (WTRU) forresetting a radio link control (RLC) entity, comprising: receiving arequest for a RLC reset in a radio resource control message;reassembling RLC service data units (SDUs) from any protocol data units(PDUs) that are received out of sequence at a receiving side of the RLCentity; discarding at the receiving side of the RLC entity any remainingPDUs that are not able to be reassembled; discarding at a transmittingside of the RLC entity all SDUs and PDUs stored in transmit buffers;stopping and resetting all timers associated with the RLC entity; andresetting all state variables associated with the RLC entity to initialvalues.
 2. The method according to claim 1, further comprising sending aRLC reset acknowledgment.
 3. The method according to claim 1, whereinthe RLC entity is an acknowledgment mode type of the RLC entity.
 4. Awireless transmit/receive unit (WTRU), comprising: a processorcomprising: a radio resource control entity configured to receive arequest for a radio link control reset in a radio resource controlmessage; and a radio link control (RLC) entity configured to reassembleradio link control service data units (SDUs) from any protocol dataunits (PDUs) that are received out of sequence at a receiving side ofthe RLC entity; to deliver reassembled SDUs in sequence to a packet dataconvergence protocol entity; to discard at the receiving side of the RLCentity any remaining PDUs that are not able to be reassembled; todiscard at a transmitting side of the RLC entity all SDUs and PDUsstored in transmit buffers; to stop and reset all timers associated withthe RLC entity; and to reset all state variables associated with the RLCentity to initial values.
 5. The WTRU according to claim 4, wherein theradio resource control entity is further configured to send a RLC resetacknowledgment for acknowledging a received RLC reset request.
 6. TheWTRU according to claim 4, wherein the radio resource control entity isfurther configured to send a RLC reset acknowledgment upon the RLCentity having completed a reset as according to the received resetrequest.
 7. The WTRU according to claim 4, wherein the RLC entity is anacknowledgment mode type of radio link control entity.